The case has been referred to the USPS Inspector General, responsible for investigating employee misconduct.

The problem was first discovered by Vincent Wright. Trying to help his neighbor clear a clogged drain, he discovered mail in the pipe, and then found the apparent source in the sewer.

"It was quite a bit of mail that I pulled out and I saw with my own eyes some more mail down in there but I wasn't sure how much," Wright said.

Residents in the neighborhood complain - until yesterday - it had been at least a week since any mail had been delivered.

In the stack Wright pulled out of the catch basin, he found bills and even a check.

Then Tuesday, DC Water said it retrieved 25 bags full of mail and handed it all off to the USPS IG's office.

In a statement, the IG's Chief of Staff Agapi Doulaveris said, "This is an unfortunate situation and we are working diligently to secure the discarded mail and continuing our investigation into the matter."

"Customers in the Northeast D.C. area who have questions regarding mail delivery can contact the Consumer Affairs Office at 202-636-1200 or 202-636-1259," Doulaveris added.

The postal service said the agency will make every effort to recover and deliver all mail as promptly as possible. Calling this an "isolated incident," a spokesperson apologized to all affected customers.